1. Field of Invention
The present invention relates to a power controlling mechanism, and more particularly, to a power control device using the battery as its power and the operating method thereof.
2. Description of Related Art
For a portable electronic device using the battery as its power (such as the digital camera, the digital still camera (DSC), or the personal digital assistant (PDA), the detection of the battery power storage is a very important issue. The conventional method directly measures the voltage between the positive pole end and the negative pole end of the battery to determine whether the voltage is higher than a predetermined cut-off voltage or not, so as to determine whether the battery power is sufficient or not.
However, the characteristic of the battery inner resistor is not the same for the different types of batteries. The alkaline battery and the Ni-MH (Nickel Metal Hydride) battery are exemplified herein for description, wherein the inner resistance of the alkaline battery is greater than the inner resistance of the Ni-MH battery. FIG. 1 is a schematic diagram of a discharging curve of the alkaline battery and the Ni-MH battery. As shown in FIG. 1, when a power consuming device in the portable electronic device is active, a battery voltage drop occurs in both the alkaline battery and the Ni-MH battery over time. Moreover, since the battery inner resistance r1 of the alkaline battery is greater than the battery inner resistance r2 of the Ni-MH battery, the battery voltage drop in the device using the alkaline battery is faster (and also as its power is greater) than the battery voltage drop occurred in the device using the Ni-MH battery.
Using the conventional method to directly measure the battery voltage, when the power consuming device is not active, the battery voltage of the portable device using the alkaline battery is detected to be higher than the cut-off voltage. However, upon the power consuming device being active, the measured voltage of the battery may fall below the cut-off voltage due to the existence of the inner resistance. Moreover, if the user is not notified that the battery power is insufficient and that the battery needs to be replaced immediately, once the power consuming device is active, the portable device may fail to operate due to insufficient power.
On the other hand, a portable electronic device using the Ni-MH battery, when using the conventional method to the measure its battery voltage, one may find that when the power consuming device is not active, the Ni-MH measured voltage is lower compared to the voltage of the portable electronic device using the alkaline battery However, due to the lower inner resistance of the Ni-MH battery, when the power consuming device is active, the voltage drop is smaller compared to the voltage drop of the alkaline battery. As a result, the battery voltage measured for the Ni-MH battery is even higher than the cut-off voltage, which indicates that the battery still has sufficient power, so the device does not need to warn the user even though there may be not enough power to operate the portable electronic device. As a consequence, measuring the battery voltage directly by using the conventional method cannot accurately detect whether the battery power is sufficient for the device to operate normally or not. Accordingly, the user may not be able to determine the exact power storage of the battery and thus cannot replace the battery immediately to avoid the device from failing to operate. Therefore, there is a need as to how to accurately detect the power storage of the battery, which has urged developers to solve this critical issue, especially important for a reliable, normal operation of portable electronic devices.